Particulate matter (PM), also known as particle pollution, can be a complex mixture of extremely small particles and liquid droplets in the air. Particles with diameters that are 10 micrometers (μm) and smaller are generally referred to as PM10, and those that are 2.5 μm and smaller are generally referred to as PM2.5. Both PM10 and PM2.5 are of particular concern due to their potential for penetrating the deepest parts (including the gas exchange regions) of the lungs and the damaging effects they can have the respiratory and cardiovascular systems.
Organizations such as the World Health Organization (WHO) and various government agencies measure and report PM levels based on PM mass concentration, which is the mass of deposited or captured particles per air sampling volume, measured in micrograms per meter cubed (μg/m3). In order to limit individual exposure to PM10 and PM2.5 mass concentrations, monitoring techniques are becoming of increasing importance worldwide.
However, existing instruments/techniques for measuring PM mass concentrations are subject to shortcomings in efficiency, high costs, and/or accuracy. For example, some PM mass concentration measurement instruments/techniques do not provide mass concentration measurements in real-time (i.e., they can report only hourly and daily averages). These instruments/techniques include those that employ a gravimetric method, a microbalance method (e.g., a tapered element oscillating microbalance (TEOM) device, a quartz crystal microbalance QCM device, and the like), and/or a beta attenuation monitoring (BAM) method to determine PM mass concentration. These instruments/techniques are also very are costly, have deployment restrictions (e.g. additional shelter), and have frequent maintenance/calibration needs. Some optical instruments/techniques (such as those based on the Lorenz-Mie-Debye solution, also referred to herein as a “Mie devices”) have been employed to measure PM information at lower costs than instruments that rely on gravimetric measurements, microbalance methods or BAM. However these optical instruments/techniques do not measure PM mass concentration. On the contrary, these optical instruments/techniques are generally only capable of measuring particle count and roughly measuring particle size.